1. Field of the Invention
This invention relates to method and apparatus for examination of ocular microcirculation and subsequent treatment to prevent, ameliorate or inhibit worsening of disease associated with abnormalities of choroidal and/or subretinal microcirculation. In particular, the invention relates to method and apparatus for diagnosis and treatment of ocular neovascularization.
2. Related Art
A pathology of current interest is age-related macular degeneration, symptoms of which include the growth of fibrovascular membranes and new blood vessels around, and from the choroid below, the macula. The prognosis is progression to eventual blindness in the aged population with this illness. The choroid is the layer below the Bruch's membrane and the retinal pigment epithelium. The neovascularization typical of this disease arises from the capillary network (called the choriocapillaris) which, for our intents and purposes, may be considered as flat in the microscopic field of view or region of interest. Diabetic retinopathy is another disease associated with neovascularization in the retina.
The progression of these diseases includes the growth of new blood vessels in the choroid and the retina. This neovascularization can occur in different layers in the fundus and may lead to blindness. These new, microscopic vessels are fragile. They may push upwards, off the plane of the normally flat choroidal capillary networks, into or against the retina (in which the light-sensing ganglion cells reside) or the Bruch's membrane or the retinal pigment epithelium, resulting in bleeding, and/or retinal detachment which may lead to blindness.
Current techniques for examining such diseases include fluorescein angiography (SF) and indocyanine green angiography (ICG). These techniques do not resolve the microscopic details which permit the earliest possible detection of the existence and the exact locations of these new vessels. The ophthalmologist requires angiographs, then time to study them, deciding on suspect areas, whether to recall the patient for confirmatory angiographs or for treatment. Also, even if visible damage is noted, separate techniques (eg laser photocoagulation) using different instruments, must then be employed for later treatment. There is therefore a delay from examination to treatment, causing inconvenience to the patient in the multiple visits required. The additional costs in the different instruments and the manpower for handling these different instruments as well as the multiple visits are disadvantages.
There are several different techniques for locating neovascularization. Some of them are still experimental or undergoing clinical trials, (eg Optical Coherence Tomography--OCT). The existing commercial devices do not provide high-resolution and/or high-magnification images. Some simply take electronic pictures of the entire fundus (at low magnification), using false colour and other image-processing means to enhance the low resolution images.
The current treatment techniques for the removal of neovascularization employ imprecise local areal destruction (usually using a laser beam) after damage becomes visible; damage is significant if it is visible even in low-magnification, low-resolution angiographs. The laser destroys the suspect neovascularization by destroying and coagulating the area surrounding the suspect neovascularization location. Other means, some still experimental, of terminating neovascularization involve invasive methods like optic fibre insertion into the vitreous chamber.
U.S. Pat. No. 4,838,679 describes an apparatus for and a method of examining the front parts of human eyes. The apparatus is specifically designed for corneal examination using light reflected from a raster-scanning laser source. The apparatus is not suitable for fundus examination and does not describe treatment of neovascularization.
U.S. Pat. No. 4,213,678 describes an apparatus for examining the fundus. Again, this is achieved using reflected light and via scanning with a laser source of light. Resolution achieved with this apparatus is not sufficient for early diagnosis of neovascularization. There is reference to treatment of the fundus using a laser but no details are provided.
Currently, no known apparatus enables examination of those parts of the eye at the macula or in the layers below it with sufficient image quality for neovascularization to be detected before visible macula damage occurs, or enables examination of those parts of the eye at or around the fovea with sufficient data for detection of feeder vessels of a neovascular net.
Further, no apparatus is known that enables early diagnosis of macular degeneration and its treatment prior to significant loss of vision.